Guggenheim analyst Yatin Suneja weighed in on Biogen (NASDAQ: BIIB) after the company and partner Eisai announced the discontinuation of the ENGAGE and EMERGE studies of aducanumab (AB antibody) in Alzheimer's, based on a futility analysis conducted by an IDMC.

"While unfortunate, we are not particularly surprised as numerous AB-targeting compounds have failed to demonstrate benefit in Alzheimer's patients, and, in our view, this trial may signal the end of the current AB hypothesis of Alzheimer's etiology," Suneja. "We expect shares to be down at least 15-20%. IP risk around Tecfidera (next overhang) to become center focus for investors."

The analyst reiterated a Neutral rating and $325.00 price target on BIIB.

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Shares of Biogen closed at $232.00 yesterday.